Vibration motor

ABSTRACT

Disclosed is a motor having a rotor driven by a vibrator generating a vibration of rope skipping motion. The rotor has a friction portion which is in contact with the friction portion of the vibrator so as to be given the vibration of rope skipping motion by the friction portion of the vibrator, and a supporting portion which is provided at a position spaced apart from the friction portion and which is in contact with a portion of the vibrator. Thus, the motor is constructed compactly.

This application is a continuation of application Ser. No. 07/836,977filed Feb. 19, 1992, now abandoned, which is a division of applicationSer. No. 07/548,673 filed Jul. 5, 1990 now U.S. Pat. No. 5,124,611.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a motor generating mechanical power withoutresorting to an electromagnetic force, and in particular to a motorwhich utilizes a circular motion excited in a vibrator by thecombination of expansion and contraction vibrations in the axialdirection to rotate a driven member coaxially fitted to the vibrator byfrictional driving.

2. Related Background Art

Vibrators of this kind are disclosed, for example, in Japanese PatentLaid-Open Application No. 62-141980 and Japanese Patent Laid-OpenApplication No. 63-214381.

Such a vibrator, as shown in FIG. 12 of the accompanying drawings,comprises a vibration member 100 comprising a metallic round bar ofcone-like shape the outer diameter of whose base portion graduallydecreases toward the fore end portion, a circular ring-like metallickeep member 101 having an outer diameter equal to that of thelarge-diameter portion of the vibration member 100, and twoelectrostrictive element plates 102, 103 as electromechanical energyconversion elements formed into a circular ring-like shape and disposedbetween the vibration member 100 and the keep member 101, the keepmember 101 being fixed to the vibration member 100 by a bolt 104, theelectrostrictive element plates 102 and 103 being urged against eachother and held thereby. The electrostrictive element plates 102 and 103each have on one surface thereof two electrodes differing in thedirection of polarization from each other and formed symmetricallydivisionally and have a common electrode on the other surface thereof,and are disposed with a positional phase of 90° each and with thedivisional electrode side as the front side. Between theelectrostrictive element plates 102 and 103, there are disposedelectrode plates 105 and 106 which are in contact with the divisionalelectrodes of the rearward electrostrictive element plate 103 and thecommon electrode of the forward electrostrictive element plate 102, andthe divisional electrodes of the forward electrostrictive element plate102 are in contact with the vibration member 100 and the commonelectrode of the rearward electrostrictive element plate 103 is incontact with a common electrode plate 107.

By AC voltages equal in both amplitude and frequency being applied tothe forward electrostrictive element plate 102 and the rearwardelectrostrictive element plate 103 with a phase difference in timetherebetween, vibration comprising the combination of the vibration ofthe electrostrictive element plate 102 and the vibration of theelectrostrictive element plate 103 is generated in the vibrator tothereby cause the fore end of the vibrator to effect circular motion.

FIG. 13 of the accompanying drawings shows a motor using such a vibratoras a drive source. The fore end of the vibrator is urged against thesurface of a disk 108, and the disk 108 is frictionally driven by thecircular motion of the fore end of the vibrator and a rotative force isoutput from a rotary shaft 109 fixed to the center of the disk 108.

Now, the motor utilizing such a vibrator utilizes the movement of thefore end portion of the vibrator, and according to my experiment, suchmotor has the difficulty that the rotational torque of the fore endportion of the vibrator is weak and a sufficient driving torque cannotbe given to the disk which is a driven member.

The following two points have been considered to be the reasonstherefor. The first point is that the fore end portion is a free endhaving no node at one side thereof and is low in rigidity and thereforesufficient vibration energy is not transmitted. The second point is thatthe free end which is the fore end is the loop of the vibration of ropeskipping motion generating a circular motion (i.e., the vibration of amotion similar to the motion of the rope in rope skipping) and at thesame time, the loop of the vibration in the axial direction. Therefore,the circular motion of the fore end in a plane perpendicular to the axiswhich is asserted by the aforementioned Japanese Patent Laid-OpenApplications Nos. 62-141980 and 63-214381 does not actually take placeand there is presented a form of frictional driving which is not smoothand in which the vibrator contacts the moving member only once perperiod of the vibration.

Also, in the case of such a motor in which the vibrator effects theaforedescribed vibration of rope skipping motion, it is necessary togive sufficient consideration also to the supporting of the drivenmember so that the motor may not become bulky.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an efficient andcompact motor or actuator.

Other objects of the present invention will become apparent from thefollowing detailed description of the invention.

In a preferred embodiment, a rotor driven by a vibrator which generatesrope skipping motion has a friction portion which is in contact with thefriction portion of the vibrator so as to be given rope skipping motionfrom the friction portion of the vibrator, and a supporting portionwhich is spaced apart from the friction portion and is in contact with aportion of said vibrator. Thus, the motor is constructed compactly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a first embodiment of amotor according to the present invention.

FIG. 2 shows the waveform of an AC power source applied to apiezo-electric element plate.

FIGS. 3A and 3B are a front view and a side view, respectively, showinga rope skipping motion of three nodes.

FIG. 4 shows the assembled state of the motor of the first embodiment.

FIGS. 5A and 5B illustrate the principle of driving, FIG. 5Aillustrating the principle on which a shaft effects rope skipping motionto rotate a hollow member, and FIG. 5B illustrating the principle onwhich a hollow vibration member effects rope skipping motion to rotate ashaft.

FIGS. 6A and 6B are a front view and a side cross-sectional view,respectively, showing a flangeless vibrator as it is supported by threebolts each having a ball-like tip end.

FIGS. 7A, 7B, 7C, 7D, 7E and 7F are views for confirming the principleof rotation.

FIG. 8 shows the relation with the positions of a vibrator with respectto the displacement of rope skipping vibration and the displacement ofvibration in the axial direction.

FIGS. 9A, 9B and 9C are cross-sectional views of a second embodiment ofthe present invention.

FIG. 10 is a cross-sectional view of a third embodiment of the presentinvention.

FIG. 11 is a cross-sectional view of a fourth embodiment of the presentinvention.

FIG. 12 is a cross-sectional view showing a vibrator according to theprior art.

FIG. 13 is a perspective view of a motor utilizing the vibratoraccording to the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an exploded perspective view of a first embodiment of a motoraccording to the present invention.

The reference numeral 1 designates a vibration member comprising ametallic round bar having a cone-shaped horn portion 1c graduallydecreasing in diameter toward the fore end portion thereof and formedbetween a small-diameter shaft portion 1a at the fore end and alarge-diameter shaft portion 1b at the rear end. Reference numeral 2denotes a keep member comprising a metallic round bar having abolt-passing hole in the axis thereof formed so as to have an outerdiameter equal to that of the large-diameter shaft portion 1b of thevibration member 1. Reference numerals 3 and 4 designate circularring-shaped piezo-electric element plates formed with an outer diameterequal to that of the large-diameter shaft portion 1b,and the referencenumeral 5 denotes the electrode plate of the piezo-electric elementplates 3 and 4. Between the vibration member 1 and the keep member 2,the piezo-electric element plates 3 and 4 are disposed with theelectrode plate 5 interposed therebetween, and the keep member 2 isfixed to the vibration member 1 by a bolt 6, whereby the piezo-electricelement plates 3 and 4 are fixed between the vibration member 1 and thekeep member 2, thus forming a vibrator A. The bolt 6 has its headbrought into contact with the keep member 2 with a circular ring-likeinsulating member 7 interposed therebetween and has its shaft portionheld in noncontact with the piezo-electric element plates 3, 4 and theelectrode plate 5.

The piezo-electric element plate 3 has on one surface thereof twoelectrodes (plus (+) electrode a and minus (-) electrode b)symmetrically formed on the opposite sides of an insulating portion dformed on the center axis position. The two electrodes differ in thedirection of polarization from each other are polarized in the directionof thickness, and have on the other surface thereof a common electrode cfor + electrode a and - electrode b electrically connected to the commonelectrode plate 5. On the other hand, the piezo-electric element plate 4has electrodes (+: electrode a and -: electrode b) disposed positionally90° out of phase with each other relative to the electrodes of thepiezo-electric element plate 3, and further has on the back thereof acommon electrode for these electrodes. The polarized electrodes (+electrode a and - electrode b) of the piezo-electric element plate 3 arein electrical contact with the rear end surface of the vibration member1 which is an electrical conductor, and the piezo-electric element plate4 is in contact with the fore end surface of the keep member 2 which isan electrical conductor.

An AC voltage V₁ is applied between the common electrode plate 5 and thevibrator 1 and an AC voltage V₂ is applied between the common electrodeplate 5 and the keep member 2, whereby the vibrator A is vibrated by thecombination of the vibration due to the expansion and contractiondisplacement of the piezo-electric element plate 3 in the direction ofthickness thereof and the vibration due to the expansion and contractiondisplacement of the piezo-electric element plate 4 in the direction ofthickness thereof.

The AC voltage V₁ from an AC voltage source V₁₀ and the AC voltage V₂from an AC voltage source V₂₀, as shown in FIG. 2, are equal in bothamplitude and frequency and are 90° out of phase with each other in timeand space.

Thus, the vibrator A effects circular motion like that of a rope of ropeskipping (hereinafter referred to as "vibration of rope skippingmotion") about the axis thereof. The principle on which such circularmotion occurs is known and therefore need not be described herein.

Here, when it is assumed that the opposite ends of the vibrator A arefree ends, the loops of the vibration of rope skipping motion are formedat the opposite ends of the vibrator A, and from the shape of thevibrator A, the diameter of the circular motion at the fore end of thevibration member 1 is larger than that at the rear end of the keepmember 2, but as previously described, the torque in the circular motionat the fore end of the vibration member 1 is small.

In the present embodiment, the vibrator A is designed such that theposition of the loop of the vibration of rope skipping motion lies atthe sliding portion B of the horn portion 1c of the vibration member inthe vibrator A, and the piezo-electric element plates 3 and 4 are drivenby the resonance frequency of the vibrator A.

That is, the vibrator A vibrates in a mode of three or more nodes asconsidered in the mode of the vibration of rope skipping motion, andvibrates with at least the opposite ends and the sliding portion B ofthe vibrator A as the loops of this vibration mode. The vibration member1 effects such rope skipping motion with the axis l of the vibrationmember 1 as the center as shown in FIGS. 3A and 3B, where the centerpoint P of the loop (H1) of the vibration of rope skipping motion of thevibration member 1 moves on the circumference of a circle c, as shown inFIG. 3A. The rope skipping motion in the sliding portion B is utilizedso that a rotor 8 which will be described later may be rotated about theaxis l, and the torque obtained in this sliding portion B is greaterthan the torque obtained in the fore end portion D.

As shown in FIG. 4, the rotor 8 as a driven member is fitted coaxiallywith the axis l of the vibrator A, the rear end portion (hereinafterreferred to as "friction contact portion") 8b of the bore portion of therotor 8 extends to a position corresponding to the sliding portion B,and the friction contact portion 8b bears against the sliding portion Bof the horn portion 1c. This horn portion 1c is provided to receive anaxial pressure force from the rotor 8 to thereby obtain an appropriatefrictional force in the sliding portion B. This sliding portion Bprovides the loop of the vibration of rope skipping motion in thevibration member 1.

In the bore portion 8a of the rotor 8 provided at a location spacedapart from the contact portion 8b, a member 8d of low coefficient offriction which is in contact with the shaft portion 1a is provided atthe position of the node of the vibration of rope skipping motion in thevibration member 1, and constitutes a support member for the rotor 8.The rotor 8 is provided with an escapement 8c to prevent sound frombeing produced relative to any vibration generated in portions otherthan the sliding portion B. This will be described later.

The friction contact portion 8b of the rotor 8 diverges into a shape inwhich the inner diameter thereof matching the outer peripheral shape ofthe sliding portion B increases gradually, and makes surface contactwith the sliding portion B during the rope skipping motion of thevibration member 1.

The rotor 8 is pushed in the direction of the arrow in FIG. 4 by aspring or the like, not shown, for example, through a thrust bearing,not shown, to thereby produce a predetermined frictional force in theportion of contact between the friction contact portion 8b and thesliding portion B, and is permitted to be rotated in the axial directionby said thrust bearing.

That is, when the vibrator A vibrates, for example, in a mode of threenodes in which the sliding portion B is the position of the loop of thisvibration mode, as previously described, the vibration member 1 effectsa rope skipping motion about the axis l as shown in FIG. 3, and as shownin FIG. 5A, the sliding portion B effects a circular motion describing alocus of a predetermined radius r in a clockwise direction or acounterclockwise direction relative to the axis l while making frictioncontact with the friction contact portion 8b of the rotor 8, thusrotating the rotor 8. That is, the rotor is driven by the same principleas the known planetary roller. In order to explain that the slidingportion B effects circular motion while rubbing against the innerperipheral surface of the friction contact portion 8b of the rotor, inFIG. 5A, the outer diameter of the sliding portion B is madeconsiderably smaller than the inner diameter of the friction contactportion 8b of the rotor 8. However, the radius of the rope skippingmotion in the sliding portion B is very slight and therefore, there is aminute clearance between the sliding portion B and the inner peripheralsurface of the friction contact portion 8b of the rotor 8. The factorswhich determine this minute clearance are the acute angle of thecone-shape of the vibration member 1 and the amount of amplitude of theaxial vibration in the sliding portion B.

Whereas in the principle of the drive transmission of the planetaryroller, it is assumed that there is-no slip between the sliding portionB and the friction contact portion 8b, when the vibration member 1 makesone full rotation by rope skipping motion, the rotor 8 rotates by anamount corresponding to the difference between the circumferentiallength of the sliding portion B and the circumferential length of thefriction contact portion 8b of the rotor 8. Because of that principle,even if the vibration member 1 is effecting a rope skipping motion at aperiod as high as 20 KHz, the number of rotations of the rotor 8 ismerely several hundred per minute at the most.

That is, noting any point 1d on the sliding portion of the vibrationmember 1, the point 1d effects a circular motion whose radius isdetermined by the aforementioned minute clearance, and contacts theinner peripheral portion of the rotor 8 in that process, therebyproviding a frictional driving force for causing the rotor 8 to effectrotational motion.

FIG. 5B, conversely to FIG. 5A, shows a case where the vibration member1 is of a cylindrical shape and the rotor 8 rotates while makingfriction contact with the hollow inner side surface of the cylindricalvibration member 1. In this case, the direction of rotation of thevibration member and the direction of rotation of the rotor are oppositeto each other.

On the other hand, the rotor 8 is provided with an escapement 8c, andthe role of this escapement to make the friction contact portion 8buniformly contact the sliding portion 1c. That is, if the innerperipheral portion 8a of the rotor 8 is too long, such that thesupporting portion which contacts the small diameter shaft portion 1a ofthe vibration member 1 becomes long, the clearance between thesmall-diameter shaft portion 1a and the inner peripheral portion 8a willbecome small. Therefore, it will be difficult for the friction contactportion 8b and the sliding portion B to contact each other uniformlywithin the allowable range of the angle of inclination of the axis ofthe rotor 8 with respect to the axis l of the vibration member. Thus, asound will be produced. So, even an attempt to solve this problem bymaking the clearance large would cause the rotor 8 to rotate with itsaxis inclined. That is, to solve the above-noted problem, there must bean appropriate positional relation between the small-diameter shaftportion 1a and the inner peripheral portion 8a of the rotor. As a resultof my experiment, it has been found that it is preferable that the innerperipheral portion 8a of the rotor be set at the position of the node ofthe vibration of rope skipping motion of the vibration member 1 with alow friction member 8d interposed between it and the small-diametershaft portion 1a. At the position of this node, no drive force isprovided to the rotor and the provision of the inner peripheral portion8a of the rotor in this node portion simply serves as a support.Therefore, no sound is produced. On the other hand, if the innerperipheral portion 8a is set at the position of the loop of thevibration of rope skipping motion in the vibration member 1, a driveforce mismatching the originally necessary drive force in the slidingportion B may be provided to the rotor 8, thus producing a sound.

Now, the vibrator A is not such that only the vibration member 1vibrates, but is such that the whole of it vibrates. Therefore, how tosupport the vibration A relative to an instrument or the like poses aproblem when mounting the motor M on the instrument or the like.

In such case, supporting the vibrator A at the position of the node ofthis vibration mode apparently seems to be best suited because of itssmall amplitude. However, since the vibrator A is effecting a ropeskipping motion starting from the position of the node of this vibrationmode, the plane perpendicular to the axis l at the position of the nodeof this vibration mode oscillates along the direction of the axis l.

Therefore, if a flange for mounting the motor is extended at a locationwhich provides the position of the node of this vibration mode in thevibrator A, for example, on the outer peripheral surface of thevibration member 1 or the keep member 2, the vibrator will not vibrateat all when the fixing method is firm. On the other hand, if asupporting method in which the attenuation of vibration is suppressedwith a member like a spring interposed between the vibration member andthe flange is adopted, the flange may oscillate in the axial directionthereof and the portion mounted on the instrument or the like may bedestroyed by vibration in the worst case, and the position of the nodeof this vibration mode is not suitable for supporting the vibrator A.

So, I have studied the vibrating state of the vibrator A and have foundthat the position of the loop of this vibration mode which apparentlyseems to be unsuitable as the supporting position for the vibrator A issuitable.

That is, at the position of the loop of this vibration mode, theamplitude is great, but displacement takes place only in the radialdirection. Therefore, there will not occur a drawback attributable tothe oscillating motion as described above. Also, the position of theloop of this vibration mode which provides the supporting position isnaturally provided axially rearwardly of the sliding portion B from thestructure of the motor M, and when the vibrator A is vibrated by athree-node mode, there is only one location which is best suited as thesupporting position. This is because although there are a total of fourpositions of the loops in this vibration mode, i.e., the opposite endsof the vibration member and two locations therebetween, the oppositeends are greatest in axial vibration and worst for fixed supporting, andone of the two loops of the vibration of rope skipping motion betweenthe opposite ends is used as the sliding portion. It has also been foundthat in the structure as shown in FIG. 6A wherein the vibrator A isprovided with no flange and is fixedly supported by three bolts 60 orthe like each having a spherical fore end with the aid of a supportingcylinder 61, the positions which provide loops in the vibration of ropeskipping motion are good positions which do not .impede vibration assupporting positions.

That is, the amplitude of the vibration in the vibrator A is very smalland the amplitude at the positions of the loops of this vibration modewhich provide these supporting positions is still smaller than theamplitude in the sliding portion B which effects the driving of therotor 8. Therefore, the radial displacement can be almost neglected, andby using the positions of the loops in the direction of vibration as thesupporting positions for the vibrator A, it becomes possible to supportthe vibrator A stably on the instrument or the like.

FIGS. 7A-7E show the results of experiments confirming theaforedescribed principle of rotation.

FIG. 7A shows the result of a test in which the direction of rotationwas examined when the fore end of the vibration member 1 was made hollowand a metal ball 30 was placed thereon. The metal ball is rotating inthe direction opposite to the direction of rotation of the rotor 8underlying it. This is because the metal ball 30 is in contact with theinner peripheral surface of the hollow portion at the fore end of thevibration member 1, and is the same as the principle already describedin connection with FIG. 5B. FIG. 7B shows the result of an experimentwhich shows that the direction of rotation when a disk-like metal plate31 is placed on the fore end of the vibration member is opposite to thedirection of rotation of the rotor 8 underlying it. The principle ofthis is shown in FIG. 7E. In FIG. 7E, it is seen that when the slidingportion B of the vibration member 1 moves toward the other side relativeto the plane of the drawing sheet, a point 1e which is in contact withthe metal plate 31 at the fore end of the vibration member 1 is the loopof vibration, like the sliding portion B. Therefore, if the plane of thedrawing sheet is regarded as a neutral plane, it moves toward this siderelative to the plane of the drawing sheet. FIG. 7C shows the directionof rotation when a rotor 32 having a convex cone-shaped portion isplaced on the fore end portion of the same vibration member 1 as thatshown in FIG. 7A. Again in this case, the rotor 32 rotates in thedirection opposite to the direction of rotation of the rotor 8underlying it, but the principle of it is the same as that described inconnection with FIG. 5B.

FIG. 7D shows the direction of rotation when a rotor 33 having a concaveconical portion is placed on the fore end of the vibration member 1.This rotor 33 rotates in the same direction as the rotor 8 underlyingit. The principle of this is shown in FIG. 7F. That is, it is seen thatwhen the sliding portion B of the vibration member 1 moves toward theother side relative to the plane of the drawing sheet, the portion 1e ofthe fore end which is in contact with the rotor 33 moves toward thisside relative to the plane of the drawing sheet.

In FIG. 8, (a)-1, (b)-1 and (c)-i are side views of vibrators whosecone-shaped portions are at 30°, 45° and 60°, respectively, and (a)-2,(b)-2 and (c)-2 show the relations between the amount of displacement ofrope skipping vibration and the axial position of the vibrator. Also,FIGS. 8(a)-3, (b)-3 and (c)-3 show the relations between the amount ofdisplacement of the vibration in the axial direction and the axialposition of the vibrator. The vibration conditions were 35.0 KHz, 35.5KHz and 35.8 KHz for the vibrators (a)-1, (b)-i and (c)-1, respectively,and the applied voltages were all 100 V_(p-p). A photo sensor was usedfor the measurement of the amount of displacement. As a result of themeasurement, the rope skipping vibration is in a three-node vibrationmode, and the vibration in the axial direction is in a two-nodevibration mode. The positions of the loops of the rope skippingvibration substantially coincided with the positions of the nodes of thevibration in the axial direction. The amount of displacement was greaterin the thinner portion of the vibrator, and as regards the amount ofdisplacement of the small-diameter part of the fore end portion, boththe rope skipping vibration and the vibration in the axial directionexhibited a maximum amount of displacement in the case of any vibrator.

It has been found that depending on the difference in the axialposition, there are broadly three kinds of differences in the form ofvibration. That is, the first is the position of the open end, and thisis the position which provides a loop both in the rope skippingvibration and in the vibration in the axial direction. The second is theposition of the node of the rope skipping vibration, and this positionsubstantially coincides with the position of the loop in the vibrationin the axial direction. The third is the position of the loop of therope skipping vibration, and this position substantially coincides withthe position of the node in the vibration in the axial direction.

When optimum positions relative to the positions of the aforementionedthree kinds of forms of vibration have been examined with respect to thefunctions necessary as a motor, i.e., effectively transmitting the driveforce to the moving member and providing the fixedly supportingposition, it has been found that the sliding portion with the movingmember is optimally the position of the loop of the rope skippingvibration, while the position for fixedly supporting the vibratorrelative to the external system of vibration is optimally the positionof the loop of the rope skipping vibration, i.e., the position whichprovides the node of the vibration in the axial direction. It has beenfound that the open end of the vibrator substantially provides theposition of the loop both in the rope skipping vibration and in thevibration in the axial direction and is worst as the fixedly supportingposition. Also, as previously described, the open end is effectingcircular motion with a certain inclination with respect to a planeperpendicular to the axis of the vibrator. Therefore, the slidingportions of the moving member and the vibration member are repeatingcontact and separation therebetween and are not effecting smoothfriction driving. Further, if an attempt is made to apply the open endto the sliding portion of the moving member, the guide portion of themoving member cannot be provided on a portion of the vibration member,and it is necessary to resort to a member which is an external system,to the vibration of the vibrator. This is because if an attempt is madeto mount, for example, a bolt or the like on a portion of the vibratorand guide the moving member, the vibration mode of the vibrator willchange. Here, supplementally describing the supporting portion 8d, inthe motor of the present invention, it is the condition of thesupporting portion 8d that the space between the sliding portion of thevibration member and the open end of the vibration member which isnearest thereto can be intactly utilized for the supporting portion 8dof the moving member. That is, the supporting portion 8d has thefunction of continuing to impart to the moving member an axis coaxialwith the axis of the vibration member.

Second Embodiment

FIGS. 9A, 9B and 9C are cross-sectional views of a second embodiment,and the motors shown in these figures are ones in which the system forurging the moving member against the vibration member is changed. Themotors of FIGS. 9A and 9B are basically identical in structure, and inthese figures, the reference numeral 18 designates a thrust bearing, andthe reference numeral 34 denotes a spring guide member adapted so that aspring may not be eccentric relative to the axis of the spring guidemember. The reference numeral 35 designates a spring for urging therotor 8 against the vibration member 1 by the expanding force of thespring when compressed. The reference numeral 36 denotes a boltthreadably engaged with the vibration member 1, and the referencenumeral 37 designates a washer. In the system of FIG. 9A, the bolt ismounted in the open end of the vibration member 1 and therefore, thebolt may readily be loosened by vibration. In the system of FIG. 9B, thebolt mounting portion is at the position of the node of the vibrationmember and, therefore, the bolt will never be loosened. FIG. 9C shows asystem in which a spring 36A is provided within the rotor to save space,and this system is of such structure that the spring 36A is tensionedbetween bolts 36 and 38 each having a hook and the contracting force ofthe spring 36A when expanded is utilized to urge the rotor 8 against thevibration member 1.

Third Embodiment

FIG. 10 is a cross-sectional view of a third embodiment.

This embodiment uses as a drive source for driving the platen roller ofa printer a motor M of the same structure as the motor M in the firstembodiment except for the shape of a rotor 8A and the supportingmechanism for the motor M. The motor M comprising a vibrator A and therotor 8A is contained in one end portion of the platen roller 10. Thismotor M is used also as a support shaft on one end side of the platenroller 10.

The motor M is such that a portion thereof which provides the loopposition of vibration is supported by the peripheral portion of a keepmember 2 for the vibrator A. A mounting flange portion 2a is provided onsaid portion and this flange portion 2a is mounted on the mounting frame11 of the printer with a low friction sheet 12 formed of a low frictionmaterial such as Teflon (trademark) being sandwiched therebetween. Ascrew 13 having a shank of a smaller diameter than the inner diameter ofa hole (not shown) formed in the flange portion 2a is threaded into saidhole, and this screw 13 is threadably coupled to the mounting frame 11,thereby restricting the movement of the motor M in the axial directionthereof, but permitting the expansion and contraction of the flangeportion 2a in the radial direction thereof.

The platen roller 10 is non-rotatably fitted to the rotor 8A of themotor M contained in the platen roller so that the rotational force ofthe rotor 8A may be directly transmitted to the platen roller, and asupport shaft 14 fixed to the other end side is journalled to themounting frame 16 of the printer for rotation and axial movement througha bearing member 15. A spring 17 is resiliently mounted on the supportshaft 14, and one end of the spring 17 bears against a thrust bearing 18and the other end of the spring 17 bears against the bearing member 15,and by the spring force of the spring 17, the rotor 8A is urged againstthe vibrator A and the roller 10 is made rotatable.

Fourth Embodiment

FIG. 11 is a cross-sectional view of a fourth embodiment. Thisembodiment is the same as the third embodiment in use, and is of suchstructure that two motors M of the first embodiment are used as a drivesource for the platen roller of a printer. As in the third embodiment, afixedly supporting flage portion 2a is provided on one of the two motorsat the same position thereon, and said one motor is fixed to a frame 11by the flange portion 2a.

The other motor is fitted to the frame 11 through a bush 39 so that themotor is freely movable in the axial direction thereof, but thevibrators themselves are prevented from rotating by a key (not shown).Further, the two vibrators have the vicinities of their fore endportions connected together by a spring 36A in the same manner as in thesystem of FIG. 9C, and by the contacting force of this spring 36A, saidtwo vibrators are urged against respective rotors 8A.

As has hitherto been described, according to the present invention, thefore end portion of the vibrator is not utilized to form the position ofthe loop of a rope skipping vibration in the horn portion, and thecircular motion of the horn portion is utilized to rotate the movingmember and therefore, the moving member can be driven with a greattorque.

In addition, in the present invention, the rotor as the driven member isbrought into contact with the vibration member at two points, i.e., thedrive force transmitting portion of the vibration member and otherportion spaced apart from said portion. Therefore, the supportingstructure for the rotor becomes simple and thus, there can be provided acompact motor or actuator.

We claim:
 1. A vibration driven motor, comprising:a vibration memberhaving a frictional contact surface; a hollow movable member having ahollow portion including a frictional contact surface which is infrictional contact with the frictional contact surface of said vibrationmember to receive a combined vibration therefrom, a portion of saidvibration member being disposable in an inner portion of said hollowportion; an electromechanical energy conversion member attached to thevibration member, for producing a combined vibration in the vibrationmember in response to an applied electrical signal, said conversionmember having a first electromechanical energy conversion element whichgenerates a first bending vibration in a first plane and a secondelectromechanical energy conversion element which generates a secondbending vibration in a second plane different from the first plane, thecombined vibration of the two vibrations causing relative movementbetween the vibration member and the movable member; and a bias memberprovided in the hollow portion of said movable member, for applying africtional contact force between said vibration member and said movablemember.
 2. A vibration driven motor according to claim 1, wherein thefirst plane is substantially perpendicular to the second plane.
 3. Avibration driven motor according to claim 1, wherein said bias memberincludes a spring.
 4. A vibration driven motor according to claim 3,wherein said spring has one end fixed to said vibration member and hasanother end fixed to a supporting member.
 5. A vibration driven motor,comprising:a vibration member including means for generating therein afirst bending vibration along a first direction and a second bendingvibration along a second direction different from the first direction, acombined vibration of the first and second bending vibrations beinggenerated therein; a hollow contact member arranged in frictionalcontact with said vibration member to receive the combined vibrationtherefrom, the combined vibration causing relative movement between thevibration member and the contact member, wherein said hollow contactmember has a hollow portion, and a portion of said vibration member isdisposable in an inner portion of said hollow portion; and a bias memberprovided within the hollow portion of said contact member, for applyinga frictional contact force between said vibration member and saidcontact member.
 6. A vibration driven motor according to claim 5,wherein the second direction is substantially perpendicular to the firstdirection.
 7. A vibration driven motor according to claim 6, whereinsaid bias member includes a spring.
 8. A vibration driven motoraccording to claim 7, wherein said spring has one end fixed to saidvibration member and has another end fixed to a supporting member.
 9. Avibration driven motor according to claim 8, further comprising:abearing for rotatably supporting said contact member, said bearing beingprovided between said vibration member and said supporting member.
 10. Avibration driven motor according to claim 9, wherein said bearing is athrust bearing contacting a side of said contact member opposite saidvibration member.
 11. A vibration driven motor according to claim 7,wherein said vibration member includes a hollow portion at a free endthereof, and wherein said spring extends through the hollow portion ofsaid vibration member.
 12. A printer comprising a platen rotatablydriven by a vibration driven motor as claimed in any one of claims 1 to11.
 13. A vibration driven motor, comprising:a vibration member having africtional contact surface; a hollow movable member having a hollowportion and a frictional contact surface which is in frictional contactwith the frictional contact surface of said vibration member to receivea combined vibration therefrom; and an electromechanical energyconversion member attached to the vibration member, for producing acombined vibration in the vibration member in response to an appliedelectrical signal, said conversion member having a firstelectromechanical energy conversion element which generates a firstbending vibration in a first plane and a second electromechanical energyconversion element which generates a second bending vibration in asecond plane different from the first plane, the combined vibration ofthe two vibrations causing relative movement between the vibrationmember and the movable member; and a bias member provided in the hollowportion of said movable member, for applying a frictional contact forcebetween said vibration member and said movable member, said bias memberincluding a spring having one end fixed to said vibration member andanother end fixed to a supporting member.
 14. A vibration driven motoraccording to claim 13, wherein the first plane is substantiallyperpendicular to the second plane.
 15. A vibration driven motor,comprising:a vibration member including means for generating a firstbending vibration along a first direction and a second bending vibrationalong a second direction different from the first direction, a combinedvibration of the first and second bending vibrations being generatedtherein; a hollow contact member having a hollow portion and arranged infrictional contact with said vibration member to receive the combinedvibration therefrom, the combined vibration causing relative movementbetween the vibration member and the contact member; and a bias memberprovided within the hollow portion of said contact member, for applyinga frictional contact force between said vibration member and saidcontact member, said bias member including a spring having one end fixedto said vibration member and another end fixed to a supporting member.16. A vibration driven motor according to claim 15, wherein the seconddirection is substantially perpendicular to the first direction.
 17. Avibration driven motor according to claim 16, further comprising:abearing for rotatably supporting said contact member, said bearing beingprovided between said vibration member and said supporting member.
 18. Avibration driven motor according to claim 17, wherein said bearing is athrust bearing contacting a side of said contact member opposite saidvibration member.
 19. A vibration driven motor, comprising:a vibrationmember including means for generating a first bending vibration along afirst direction and a second bending vibration along a second directiondifferent from the first direction, a combined vibration of the firstand second bending vibrations being generated therein, said vibrationmember including a hollow portion at a free end thereof; a hollowcontact member having a hollow portion and arranged in frictionalcontact with said vibration member to receive the combined vibrationtherefrom, the combined vibration causing relative movement between thevibration member and the contact member; and a bias member providedwithin the hollow portion of said contact member, and including a springfor applying a frictional contact force between said vibration memberand said contact member.
 20. A vibration driven motor according to claim19, wherein the second direction is substantially perpendicular to thefirst direction.
 21. A printer comprising a platen rotatably driven by avibration driven motor as claimed in any one of claims 13 to
 20. 22. Avibration driven motor, comprising:a vibration member having africtional contact surface; a hollow movable member including a hollowportion and having a frictional contact surface which is in frictionalcontact with the frictional contact surface of said vibration member toreceive a combined vibration therefrom, a portion of said vibrationmember being disposable in an inner portion of said hollow portion; anelectromechanical energy conversion member attached to the vibrationmember, for producing a combined vibration in the vibration member inresponse to an applied electrical signal, said conversion member havinga first electromechanical energy conversion element which generates afirst bending vibration in a first plane and a second electromechanicalenergy conversion element which generates a second bending vibration ina second plane different from the first plane, the combined vibration ofthe first and second vibrations causing the frictional contact surfaceof said vibration member to move in a continuous orbital movement aboutan axis of said vibration member, thereby causing relative movementbetween the vibration member and the movable member; and a bias memberprovided in the hollow portion of said movable member, for applying africtional contact force between said vibration member and said movablemember.
 23. A vibration driven motor, comprising:a vibration memberhaving a contact surface and means for generating therein a firstbending vibration along a first direction and a second bending vibrationalong a second direction different from the first direction, a combinedvibration of the first and second bending vibrations being generatedtherein, whereby the contact surface of said vibration member moves in acontinuous orbital movement about an axis of said vibration member; ahollow contact member having a hollow portion and arranged in frictionalcontact with the contact surface of said vibration member to receive thecombined vibration therefrom, the combined vibration causing relativemovement between the vibration member and the contact member; and a biasmember provided within the hollow portion of said contact member, forapplying a frictional contact force between said vibration member andsaid contact member.
 24. A vibration driven motor according to claim 23,wherein the second direction is substantially perpendicular to the firstdirection.
 25. A vibration driven motor according to claim 24, whereinsaid bias member includes a spring.
 26. A vibration driven motoraccording to claim 25, wherein said spring has one end fixed to saidvibration member and has another end fixed to a supporting member.
 27. Avibration driven motor according to claim 26, further comprising:abearing for rotatably supporting said contact member, said bearing beingprovided between said vibration member and said supporting member.
 28. Avibration driven motor according to claim 27, wherein said bearing is athrust bearing contacting a side of said contact member opposite saidvibration member.
 29. A vibration driven motor according to claim 27,wherein said vibration member includes a hollow portion at a free endthereof, and wherein said spring extends through the hollow portion ofsaid vibration member.